Thank you for your question, Corrine.  There are (at least) two fungal diseases which infect susceptible plants such as boxwood (Buxus).  You can read about them here:  Pachysandra-Box Blight | Pacific Northwest Pest Management Handbooks (pnwhandbooks.org)

and Boxwood (Buxus spp.)-Leaf Spots | Pacific Northwest Pest Management Handbooks (pnwhandbooks.org)

Unfortunately, I am unable to distinguish them on the basis of your photos.  I suggest you contact the OSU Plant Disease Clinic to submit a sample, and request recommendations, which they can do for a modest fee.   This webpage has information on contacting them, submitting samples, and the fee schedule.  | College of Agricultural Sciences | Oregon State University

I hope this is helpful.  Good luck!